4. LED Cont..
An LED (Light Emitting Diode) emits light
when an electric current passes through it.
The simplest circuit to power an LED is a
voltage source with a resistor and an LED in
series. Such a resistor is often called a ballast
resistor.
The ballast resistor is used to limit the current
through the LED and to prevent that it burns.
𝑅 =
𝑉 − 𝑉𝐿𝐸𝐷
𝐼
5. An LED with a voltage of 2 volts and an
amperage of 20 mili-amperes must be
connected to a 12 volts supply. What is
the resistance value..
𝑅 =
𝑉 − 𝑉𝐿𝐸𝐷
𝐼
=
12 − 2
0.03
= 333
6. Two LEDs are connected in series. One
red LED with a voltage of 2V and a blue
LED with 4.5 volts. Both have a rated
amperage of 30 mA.
𝑅 =
𝑉 − 𝑉𝐿𝐸𝐷1 − 𝑉𝐿𝐸𝐷2
𝐼
=
12 − 2 − 4.5
0.03
= 183.3
8. Transistor Cont..
The Transistor is the fundamental building
block of modern electronic devices in
modern electronic systems.
A transistor is an electronic component
used in a circuit to control a large
amount of current or voltage with a
small amount of voltage or current.
This means that it can be used to amplify
or switch (rectify) electrical signals or
power, allowing it to be used in a wide
array of electronic devices.
12. Relay
A relay is an electromagnetic switch
operated by a relatively
small electric current that can turn on or
off a much larger electric current.
The heart of a relay is an electromagnet
(a coil of wire that becomes a
temporary magnet when electricity flows
through it).
13. Why is Relay useful?
As the name suggests, many sensors are
incredibly sensitive pieces of electronic
equipment and produce only small
electric currents. But often we need
them to drive bigger pieces of
apparatus that use bigger currents.
Relays bridge the gap, making it possible
for small currents to activate larger ones.
15. Electrical Relays
Electrical relays and contactors use a low level control
signal to switch a much higher voltage or current
supply using a number of different contact
arrangements
SPST – Single Pole Single Throw
SPDT – Single Pole Double Throw
DPST – Double Pole Single Throw
DPDT – Double Pole Double Throw